The present invention relates to an electrochemical cell and, more particularly, to a primary electrochemical cell for high-rate, low-temperature applications.
There are many situations in which it is desirable to utilize a primary electrochemical cell, such as a cylindrical electrochemical cell, in a high-rate, low-temperature application, for example, at a rate greater than 1 mA/cm.sup.2 and a temperature to -40.degree. C. The most common design of a high-rate cylindrical primary electrochemical cell includes a combination of an anode, a cathode electrode structure, and a separator. These elements are rolled up together, with the separator being sandwiched between the anode and the cathode electrode structure. A typical implementation of a spiral-wound, or "jelly-roll", structure as decribed above includes an anode of an oxidizable alkali metal such as lithium (within a supporting metal grid), a cathode electrode structure comprising a metal current collector (e.g., a nickel grid or screen) physically supporting an aggregation of porous carbon globules or conglomerates, and a separator of an electrically-nonconducting material such as fiberglass. These cell components normally are in a form prior to assembly of elongated rectangular strips. The arrangement of cell components as described above is utilized within the cell with a suitable electrolytic solution. A common electrolytic solution for a primary electrochemical cell is a cathodelectrolyte solution including a reducible soluble cathode such as thionyl chloride and an electrolyte solute such as lithium tetrachloroaluminate dissolved in the thionyl chloride. During the discharge of the cell having the abovedescribed components and specific materials, a progressive depletion of the lithium anode takes place as electrochemical reaction occurs within the cell and discharge products are formed. This action is normally accompanied by the generation of a small and tolerable amount of heat in the cell, more particularly, in the region of the cathode structure.
While a cylindrical spiral-wound electrochemical cell as described hereinabove operates in a generally satisfactory manner, the cell is subject to substantial IR (internal resistance) losses due to the lengths of the electrodes. As a result, there is non-uniform and incomplete utilization of the active material of the cell and, thus, a limitation on the rate of discharge of the cell and the temperature at which the cell will operate in its intended and desired fashion. In addition, the spiral-wound nature of the components of the cell tends to lead to the retention of heat developed in the cell during discharge of the cell, limiting the degree to which the heat can be effectively dissipated away from the interior of the cell to the outside, specifically, to the metal can or housing of the cell. An excessive buildup of heat within the cell can, in severe cases, lead to extensive physical damage to the cell.